Perfect Number Program in Java

In this section, we will learn what is a perfect number in Java and also create Java programs to check if the given number is perfect or not. Also, we will create a Java program for finding all the perfect numbers between the given range. The perfect number program frequently asked in Java coding tests and academics.

What is a perfect number in Java?

A number whose sum of factors (excluding the number itself) is equal to the number is called a perfect number. In other words, if the sum of positive divisors (excluding the number itself) of a number equals the number itself is called a perfect number. Let’s understood it through an example.

Example of a Perfect Number

Let’s take the number 496 and heck it is a perfect number or not.

First, we find the factors of 496 i.e. 1, 2, 4, 8, 16, 31, 62, 124, and 248. Let’s find the sum of factors (1 + 2 + 4 + 8 + 16 + 31 + 62 + 124 +248 = 496). We observe that the sum of factors is equal to the number itself. Hence, the number 496 is a perfect number. Similarly, we can check other numbers also.

Perfect Number Program in Java

Some other perfect numbers are 6, 8128, 33550336, 8589869056, etc.

Steps to Find Perfect Number

Read or initialize a number (n).
Declare a variable (s) for storing sum.
Find the factors of the given number (n) by using a loop (for/ while).
Calculate the sum of factors and store it in a variable s.
Compare the sum (s) with the number (n):
- If both (s and n) are equal, then the given number is a perfect number.
- Else, the number is not a perfect number.

Let’s implement the above steps in a Java program.

Perfect Number Java Programs

There are the following ways to find the perfect number in Java:

Using while Loop
Using Method
Using Recursion

Using while Loop

PerfectNumberExample1.java

  import java.util.Scanner;  public class PerfectNumberExample1  {  public static void main(String args[])  {  long n, sum=0;  Scanner sc=new Scanner(System.in);      System.out.print(“Enter the number: “);  n=sc.nextLong();  int i=1;  //executes until the condition becomes false  while(i <= n/2)  {  if(n % i == 0)  {  //calculates the sum of factors  Sum = sum + i;  } //end of if  //after each iteration, increments the value of variable i by 1  i++;  } //end of while  //compares sum with the number  if(sum==n)  {  //prints if sum and n are equal  System.out.println(n+” is a perfect number.”);  } //end of if  else  //prints if sum and n are not equal  System.out.println(n+” is not a perfect number.”);   }  }  

Output 1:

Enter the number: 28  28 is a perfect number.

Output 2:

Enter the number: 4558  4558 is not a perfect number.

Using Method

PerfectNumberExample2.java

  import java.util.Scanner;  public class PerfectNumberExample2  {  //function that checks if the given number is perfect or not  static long isPerfect(long num)  {  //variable stores the sum      long sum=0;  //executes until the condition becomes false  for(int i=1; i <= num/2; i++)  {  if(num % i == 0)  {  //calculates the sum of factors  sum=sum + i;  } //end of if  }  //end of for  //returns the sum of factors  return sum;  } //end of method  public static void main(String args[])  {  long number, s;  Scanner sc=new Scanner(System.in);      System.out.print(“Enter the number: “);  //reads a number from the user  number=sc.nextLong();  //calling the function  s = isPerfect(number);  //compares sum with the number  if(s==number)  System.out.println(number+” is a perfect number”);  else  System.out.println(number+” is not a perfect number”);   }   }  

Output 1:

Enter the number: 6  6 is a perfect number.

Output 2:

Enter the number: 1234  1234 is not a perfect number.

Using Recursion

PerfectNumberExample3.java

  import java.util.Scanner;  public class PerfectNumberExample3  {   static long sum=0;  long isPerfect(long num, int i)  {  //executes until the condition becomes false      if(i <= num/2)  {  if(num % i ==0)  {  //calculates the sum of factors      sum=sum + i;  }  //after each iteration, increments the value of variable i by 1  i++;  //recursively called function  isPerfect(num, i);  }  //returns the sum of factors  return sum;  }  //driver code  public static void main(String args[])  {  long number, s;  int i=1;  Scanner sc=new Scanner(System.in);      System.out.print(“Enter the number: “);  //reads a number from the user  number=sc.nextLong();  //creating an object of the class  PerfectNumberExample3 pne=new PerfectNumberExample3( );  s = pne.isPerfect(number, i);  //compares sum with the number  if(s == number)  //prints if the s and number are equal  System.out.println(number+” is a perfect number”);  else  //prints if s and number are not equal  System.out.println(number+” is not a perfect number”);   }   }  

Output 1:

Enter the number: 8128  8128 is a perfect number.

Output 2:

Enter the number: 7866  7866 is a perfect number.

Perfect Numbers Between Given Range

The following program finds all the perfect numbers between a given range.

PerfectNumberExample3.java

  public class PerfectNumberExample3  {  //function checks if the given number is perfect or not  static boolean isPerfectNumber(int num)  {  //variable stores the sum of divisors  int sum = 1;  //determines all the divisors of the given number and adds them  for (int i = 2; i * i <= num; i++)  {  if (num % i==0)  {  if(i * i != num)  sum = sum + i + num / i;  else  //calculates the sum of factors  sum = sum + i;  }  //end of if  }  //end of for  if (sum == num && num != 1)  //returns true if both conditions (above) returns true  return true;  //returns false if any condition becomes false  return false;  } //end of function  //driver code  public static void main (String args[])  {  System.out.println(“Perfect Numbers between 2 to 10000 are: “);  //loop executes until the condition n<10000 becomes false  for (int n = 2; n < 10000; n++)  //calling function  if (isPerfectNumber(n))  //prints all perfect number between given range  System.out.println(n +” is a perfect number”);  }  }  

Output:

Perfect Numbers between 2 to 10000 are:   6 is a perfect number  28 is a perfect number  496 is a perfect number  8128 is a perfect number

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Perfect Number Program in Java

Perfect Number Program in Java

What is a perfect number in Java?

Example of a Perfect Number

Steps to Find Perfect Number

Perfect Number Java Programs

Using while Loop

Using Method

Using Recursion

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